Randomised controlled trial (RCT)
/RCT (randomized controlled trial)/
Also known as: randomized controlled trial, RCT, clinical trial, gold standard trial
Definition
A randomised controlled trial is the gold standard study design in clinical research for evaluating the efficacy and safety of an intervention. In an RCT, participants are randomly allocated to either an experimental group (receiving the test compound) or a control group (receiving a placebo, standard treatment, or alternative intervention). The random allocation process reduces selection bias and helps ensure that the treatment and control groups are similar in their baseline characteristics. RCTs are designed to answer specific research questions through careful measurement of predefined outcomes, often employing double-blinding (where both participants and researchers are unaware of who receives the test treatment) to further reduce bias. The rigorous design of RCTs makes them the most convincing evidence for establishing whether a compound produces the claimed benefits.
RCTs are characterized by several key design features: random allocation, a defined sample size calculated to detect clinically meaningful differences, blinded outcome assessment, and prospective outcome registration to prevent selective reporting. Parallel-group RCTs assign participants to treatment or control for the entire study duration, while crossover RCTs have participants receive both treatments in sequence (useful when studying the same person under different conditions). Researchers must carefully define eligibility criteria, primary and secondary outcome measures, and statistical analysis plans before data collection.
The evidence hierarchy used in evidence-based medicine places RCTs at the top (along with systematic reviews of RCTs) because their design minimizes sources of bias. However, RCTs have limitations: they are expensive and time-consuming, they may recruit unrepresentative populations, and outcomes measured in controlled research settings may not fully reflect real-world effectiveness. Meta-analyses synthesize results across multiple RCTs to provide comprehensive evidence summaries.